Left 4 Dead 2 Beta

Admittedly, I'm new to Ubuntu and installed it less than 24 hours ago, so pardon the inexperience. When I startup L4D2, an error message appears and proceeds to run off of the screen, strobing. It reads: "This application requires either the GL_EXT_texture compression_s3tc, or the GL_EXT_texture_compression_dxt1 + GL_ANGLE_texture_compression_dxt3 + GL_ANGLE_texture compression_dxt5 OpenGL extensions. Please install S3TC texture support."The obvious answer appears to be to install whatever that is, but what do I do with this information? The Internet yields no results.Thank you, and I apologize again for my ineptness in pretty much everyhing.